Process for the stabilization of acrylic fibers

ABSTRACT

A process is provided wherein the thermal stabilization of an acrylic fibrous material is accelerated by heating in an oxygencontaining atmosphere following treatment while in contact with an aqueous solution wherein a substantial quantity of molecular oxygen is generated in intimate association with the fibrous material through the catalyzed decomposition of hydrogen peroxide. The resulting stabilized fibrous materials are nonburning when subjected to an ordinary match flame, and may be utilized as fire resistant textile fibers, or optionally converted to a carbonized fibrous material by heating in an inert atmosphere at a more highly elevated temperature.

llnited States Patent Riggs 54] PROCESS FOR THE STABILIZATION 3,104,934 9/1963 Blumenkopf ..8/1 15.5 CF ACRYLIC FIBERS 3,188,165 6/1965 Magat et al. ..s/115.5 [72] Inventor: John Perry Riggs, Berkeley Heights, NJ. Primary ExaminerGeorge F Lesmes [73] Assignee: Celanese Corporation, New York, NY. Assistant Examiner-John C p Filed: Mar. 1970 'ttlzlrgslylg'l'homas J. Morgan, Charles B. Barns and Kenneth [21] Appl. No.: 17,968

ABSTRACT [52] U.S. Cl ..8/l15.5, 23/209.1 F A process is provided wherein the thermal stabilization of an [5 l Int. Cl. ..D06m 9/00 acrylic fibrous material isaccelerated by heating in an oxygen- [58] Field of Search ..8/1 15.5; 23/209.l F containing atmosphere following treatment while in contact with an aqueous solution wherein a substantial quantity of References Cited molecular oxygen is generated in intimate association with the fibrous material through the catalyzed decomposition of UNITED STATES PATENTS hydrogen peroxide. The resulting stabilized fibrous materials 3,292,991 12/1966 Crawley ..8/l15.7 are non-burning when subjected to an ordinary match flame, 2,663,612 3 Geleson a 34 and may be utilized as fire resistant textile fibers, or optionally 3,539,295 1970 Ram converted to a carbonized fibrous material by heating in an 2,639,195 1 5 M tone 65 inert atmosphere at a more highly elevated temperature. 3,497,318 2/1970 Noss 23/209.l 3,418,066 12/1968 Caldwell ..8/1 15.5 20 Claims, No Drawings BACKGROUND OF THE INVENTION 1n the past procedures have been proposed for the conversion of fibers formed from acrylic polymers to a modified form possessing enhanced thermal stability. Such modification has generally been accomplished by heating the fibrous material in an oxygen-containing atmosphere at a moderate temperature for an extended period of time.

U.S. Pat. Nos. 2,913,802 to Barnett and 3,285,696 to Tsunoda disclose processes for the conversion of fibers of acrylonitrile homopolymers or copolymers to a heat resistant form. The stabilization of fibers of acrylonitrile homopolymers and copolymers in an oxygen-containing atmosphere involves (1) an oxidative cross-linking reaction of adjoining molecules as well as (2) a cyclization reaction of pendant nitrile groups. It is generally recognized that the rate at which the stabilization reaction takes place increases with the temperature of the oxygen-containing atmosphere. However, the stabilization reaction must by necessity be conducted at relatively low temperatures (i.e. below about 3001 C.), since the cyclization reaction is exothermic in nature and must be controlled if the original fibrous configuration of the material undergoing stabilization is to be preserved. Accordingly, the stabilization reaction tends to be time consuming, and economically demanding because-of low productivity necessitated by the excessive time requirements. Prior processes proposed to shorten the period of time required for the stabilization reaction include that disclosed in U.S. Pat. No. 3,416,874.

While stabilized acrylic fibrous materials may be used directly in applications where a non-buming fiber is required, demands for the same have been increasingly presented by manufacturers of carbonized fibrous materials. Carbonized fibrous materials are commonly formed by heating a stabilized acrylic fibrous material in an inert atmosphere, such as nitrogen or argon, at a more highly elevated temperature. During the carbonization reaction elements present in the fiber such as nitrogen, oxygen, and hydrogen are substantially expelled. Accordingly, the term carbonized" fibrous material as used in the art commonly designates a fibrous material consisting of at least about 90 percent carbon by weight, and generally at least about 95 percent carbon by weight. Depend ing upon the conditions under which the carbonized fibrous material is processed, it may or may not contain graphitic carbon as determined by the characteristic x-ray diffraction pattern of graphite. See, for instance, commonly assigned U.S. Ser. No. 777,275, filed Nov. 20, 1968 of Charles M. Clarke for a preferred procedure for forming carbonized and graphitized fibrous materials from a stabilized acrylic fibrous material.

It is an object of the invention to provide an improved process for enhancing the thermal stability of an acrylic fibrous material.

lt is an object of the invention to provide a process wherein the oxidative cross-linking reaction in the stabilization of an acrylic fibrous material is accelerated.

It is an object of the invention to provide a process for producing a stabilized acrylic fibrous material wherein the oxidative cross-linking reaction yields a highly uniform stabilized structure.

It is another object of the invention to provide a stabilized acrylic fibrous material which is highly amenable for utilization as a precursor in the formation of amorphous carbon or graphitic carbon fibrous materials.

lt is a further object of the invention to provide a process for the stabilization of acrylic fibrous materials which is readily adaptable to fibers of varying deniers. I

These and other objects, as well as the'scope, nature and utilization of the invention will be apparent from the following detailed description and appended claims.

2 SUMMARY OF THE lNVEN'l'lON It has been found that an improved process for the stabilization of an acrylic fibrous material selected from the group consisting of an acrylonitrile homopolymer and acrylonitrile copolymers containing at least about 85 mol percent of acrylonitrile units and up to about 15 mol percent of one or more monovinyl units copolymerized therewith comprises:

a. contacting the acrylic fibrous material with an aqueous solution wherein a substantial quantity of molecular oxygen 'isgenerated in intimate association with the acrylic fibrous material through the catalyzed decomposition of hydrogen peroxide, and

b. heating the resulting acrylic fibrous material in an oxygen-containing atmosphere at a temperature of about 200 to 290 C. until a stabilized product is formed which retains its original fibrous configuration essentially intact and which is non-burning when subjected to an ordinary match flame.

The resulting stabilized acrylic fibrous materials commonly exhibit a bound oxygen content of at least about 7 percent by weight, and a carbon content of about to 65 percent by weight.

DESCRIPTION OF PREFERRED EMBODIMENTS The acrylic fibrous materials undergoing stabilization in the present process may be formed by conventional solution spinning techniques (i.e., may be dry spun or wet spun), and are commonly drawn to increase their orientation. As is known in the art, dry spinning is commonly conducted by dissolving the polymer in an appropriate solvent, such as N,N- dimethyl forrnamide or N,N-dimethyl acetamide, and passing the solution through an opening of predetermined shape into an evaporative atmosphere (e.g., nitrogen) in which much of the solvent is evaporated. Wet spinning is commonly conducted by passing a solution of the polymer through an opening of predetermined shape into an aqueous coagulation bath.

The acrylic polymer utilized as the starting material is formed primarily of recurring acrylonitrile units. For instance, the acrylic polymer should generally contain not less than about 85 mol percent of acrylonitrile units and not more than about 15 mol percent of units derived from a monovinyl compound which is copolymerizable with acrylonitrile such as styrene, methyl acrylate, methyl methacrylate, vinyl acetate,

" .vinyl chloride, vinylidene chloride, vinyl pyridine, and the like, or a plurality of such monomers.

The preferred acrylic fibrous material is an acrylonitrile homopolymer. Preferred acrylonitrile copolymers contain at least about 95 mol percent of acrylonitrile units and up to about 5 mol percent of one or more monovinyl units copolymerized therewith.

The acrylic fibrous materials are provided as continuous lengths and may be in a variety of physical configurations. For instance, the acrylic fibrous materials may be present in the form of continuous lengths of multifilament yarns, tows, tapes, strands, cables, or similar fibrous assemblages.

When the starting material is a continuous multifilament yarn, a twist may be imparted to the same to improve the handling characteristics. For instance, a twist of about 0.1 to 5 t.p.i., and preferably about 0.3 to 1.0 t.p.i. may be utilized.

Also, a false twist may be used instead of or in addition to a real twist. Alternatively, one may select bundles of fibrous material which possess essentially no twist.

The starting material may be drawn in accordance with conventional techniques in order to improve its orientation. For instance, the starting material may be drawn by stretching while in contact with a hot shoe at a temperature of about to C. Additional representative drawing techniques are disclosed in U.S. Pat. Nos. 2,455,173; 2,948,581; and 3,122,412. It is recommended that the acrylic fibrous materials selected for use in the process be drawn to a single filament tenacity of at least about 3 grams per denier. If desired, however, the starting material may be more highly oriented, e.g.

drawn up to a single filament tenacity of about 7.5 to 8 grams per denier, or more.

Prior to heating the acrylic fibrous material in an oxygencontaining atmosphere to accomplish the desired stabilization (as described hereafter), the fibrous material is contacted with an aqueous solution wherein a substantial quantity of molecular oxygen is generated in intimate association with the acrylic fibrous material through the catalyzed decomposition of hydrogen peroxide.

The decomposition of hydrogen peroxide to yield molecular oxygen may be catalyzed by a variety of substances including those which are commonly recognized in the art to be capable of performing such a function. In a preferred embodiment of the invention the decomposition is catalyzed by the presence within the aqueous solution of certain metallic cations such as iron, copper, vanadium, nickel, chromium, manganese, and the like. The source compounds from which the metallic cations are derived upon dissolution in an aqueous solution may be widely varied as will be apparent to those skilled in the art. The only requirement being that the metallic compounds exhibit sufficient water-solubility to impart a catalytic quantity of the metallic cations to the aqueous solution.

In a preferred embodiment of the invention the metallic cations are ferrous cations which react with hydrogen peroxide in accordance with the Haber-Weiss mechanism to yield molecular oxygen. The ferrous cations may be derived from water-soluble iron compounds such as ferrous sulfate [FeSo 7H- O Ferrous cl loride [FeCl H O], ferrous nitrate [Fe(NO )'6l-I O], ferrous ammonium sulfate [FeS '(NH Q 50 -6H1O],ferrous acetate [Fe(C,I-I O '4H O],ferrous magnesium sulfate [FeSO 'MgSO -6H O], and the like. The particularly preferred water-soluble iron compound is ferrous sulfate [FeSO '7l-I O].

In a preferred embodiment of the invention the acrylic fibrous material is provided in intimate association with metallic cations capable of catalyzing the decomposition of hydrogen peroxide, and is then contacted with an aqueous solution of hydrogen peroxide wherein a substantial quantity of molecular oxygen is generated in intimate association with the acrylic fibrous material.

The intimate association of the acrylic fibrous material and the metallic cations capable of catalyzing the decomposition of hydrogen peroxide is preferably accomplished by contacting the fibrous material with a solution containing the metallic cations dissolved therein, and subsequently drying the fibrous material whereby the solvent in contact with the acrylic fibrous material is substantially expelled.

The solution from which the metallic cations are applied is preferably aqueous in nature. Solvents other than water, which are capable of dissolving the source compounds for the metallic cations, may likewise be selected provided the solvents do not adversely influence the properties of the acrylic fibrous material. In a preferred embodiment of the invention compounds capable of yielding the metallic cations upon dissolution (e.g. ferrous sulfate) are dissolved in water in concentrations of about 0.01 to 10 percent, or more, by weight.

The temperature of the solution containing the metallic cations while contacted with the acrylic fibrous material may be from below ambient up to below that temperature at which the properties of the acrylic fibrous material are adversely infiuenced. In a preferred embodiment of the invention the acrylic fibrous material is contacted with an aqueous solution of the metallic cations which is at a temperature of about 10 to 95 C. In a particularly preferred embodiment of the invention the solution is conveniently provided at ambient temperature (i.e. at about 25 C.).

The technique employed to make contact between the acrylic fibrous material and the solution of the metallic cations may be varied as will be apparent to those skilled in the art. In a preferred embodiment of the invention contact is made by immersing the acrylic fibrous material in a vessel containing a solution of the metallic cations. Alternatively, contact may be made by spraying the acrylic fibrous material with a solution of the metallic cations. The duration of the period of contact between the acrylic fibrous material and the solution is not critical provided the requisite catalytic quantity of the metallic cations is ultimately provided in intimate association with the fibrous material upon drying. For instance, the quantity of the metallic cations, provided in intimate association with the acrylic fibrous material may be from about 0.0001 to 0.5 percent by weight based upon the weight of the dried acrylic fibrous material. The duration of the period of contact will be influenced to some degree by the metallic cation concentration of the solution, the temperature of the solution, the degree of compaction of the acrylic fibrous material undergoing treatment, and the denier of the acrylic fibrous material. Contact times of about 5 seconds to 48 hours, or more, may be selected. A greater diffusion of the metallic cations into the acrylic fibrous material occurs with longer residence times. A continuous length of the acrylic fibrous material may be wound upon a support and statically contacted with the solution containing the metallic cations. Alternatively, a continuous length of the acrylic fibrous material may be continuously passed in the direction of its length through a vessel or zone in which the solution is provided.

The drying of the fibrous material following contact with the solution containing the metallic cations may be conducted in any convenient manner. For instance, the fibrous material may be simply exposed to ambient conditions until the solvent adhering thereto is substantially evaporated. The drying step can, of course, be expedited by exposure to a circulating gaseous atmosphere provided at an elevated temperature, as will be apparent to those skilled in the art. Upon removal of the solvent a thin catalytic residue of metallic cations is deposited upon the fiber surface. Also, internal diffusion of the metallic cations into the fibrous material is achieved.

In order to generate a substantial quantity of molecular oxygen in intimate association with the acrylic fibrous material, the fibrous material while bearing a residue of the metallic cations is contacted with an aqueous solution of hydrogen peroxide which is preferably provided at ambient temperature, i.e. at about 25 C. The hydrogen peroxide is preferably present in the aqueous solution in a concentration of about 3 to 30 percent by weight, and most preferably in a concentration of about 15 percent by weight. The period of time during which molecular oxygen is generated in intimate association with the acrylic fibrous material may be varied from about 10 minutes to 48 hours, or more. As discussed hereafter, the molecular oxygen becomes combined with the acrylic fibrous material by hydrogen bonding and aids in the acceleration of the subsequent stabilization step.

In an alternate preferred embodiment of the invention the acrylic fibrous material is initially provided in intimate association with hydrogen peroxide prior to being contacted with an aqueous solution containing metallic cations capable of catalyzing the decomposition of hydrogen peroxide wherein a substantial quantity of molecular oxygen is generated in intimate association with the acrylic fibrous material.

The intimate association of the acrylic fibrous material and hydrogen peroxide is preferably accomplished by contacting the fibrous material with an aqueous solution of hydrogen peroxide. The hydrogen peroxide is preferably provided in the aqueous solution in a concentration of about 3 to 30 percent by weight, and most preferably in a concentration of about l5 percent by weight. Contact times of about 5 seconds to 48 hours, or more, may be selected. It is preferred, however, that contact times of at least about 1 hour be utilized to assure complete diffusion into the acrylic fibrous material. Contact may be made by immersion, spraying, or any other convenient means. The acrylic fibrous material after contact with the aqueous solution of hydrogen peroxide optionally may be next dried by exposure to ambient conditions.

The resulting acrylic fibrous material is subsequently contacted with an aqueous solution containing metallic cations capable of catalyzing the decomposition of the hydrogen peroxide. The aqueous solution of metallic cations may be identical to those previously described. Contact may be made by immersion, spraying, or any other convenient means. The period of time during which molecular oxygen is generated in intimate association with the acrylic fibrous material upon contact with the metallic cations may be varied from about 10 minutes to 48 hours, or more. As discussed hereafter, the molecular oxygen becomes combined with the acrylic fibrous material by hydrogen bonding and serves to accelerate the stabilization step. I

The acrylic fibrous material following the generation of a substantial quantity of molecular oxygen in close proximity thereto is exposed to an oxygen-containing atmosphere at a temperature of about 200 to 290C. until a stabilized fibrous product is formed. In a preferred embodiment of the invention, the oxygen-containing atmosphere is air. Preferred temperatures for the oxygen-containing atmosphere are about 220 to 260 C., and most preferably about 240 to 250 C.

For best results, uniform contact during the stabilization reaction with molecular oxygen throughout all portions of the acrylic fibrous materials is encouraged. Such uniform reaction I conditions can best be accomplished by limiting the mass of fibrous material at any one location so that heat dissipation from within the interior of the fibrous material is not unduly impaired, and free access to molecular oxygen is provided. For instance, the acrylic fibrous material may be placed in the oxygen-containing atmosphere while wound upon a support to a limited thickness. In a preferred embodiment of the invention, the acrylic fibrous material is continuously passed in the direction of its length through the heated oxygen-containing atmosphere. For instance, a continuous length of the acrylic fibrous material may be passed through a circulating oven or the tube of a muffle furnace. The speed of passage through the heated oxygencontaining atmosphere will be determined by the size of the heating zone and the desired residence time.

The period of time required to complete the stabilization reaction within the oxygen-containing atmosphere is generally inversely related to the temperature of the atmosphere, and is also influenced by the denier of the acrylic fibrous material undergoing treatment. Treatment times in the oxygen-containing atmosphere accordingly commonly range from about 30 minutes to 100 hours. Regardless of the stabilization temperature selected within the range of about 200 to 290 C., the presence of the acrylic fibrous material in modified form resulting from its treatment heretofore described results in an accelerated oxidative cross-linking reaction for a given tem perature.

The stabilized acrylic fibrous materials formed in accordance with the present process are black in appearance, retain essentially the same fibrous configuration as the starting material, are non-burning when subjected to an ordinary match flame, commonly have a bound oxygen content of at least 7 percent by weight as determined by the Unterzaucher analysis, and commonly contain from about 50 to 65 percent carbon by weight.

The theory whereby the prior treatment of the acrylic fibrous material through the generation of molecular oxygen in intimate association therewith aids in the subsequent stabilization reaction which is conducted in an oxygen-containing atmosphere is considered complex and incapable of simple explanation. It is believed, however,'that the prior treatment results in molecular oxygen being hydrogen bonded to the acrylic polymer which is capable of enhancing the rate at which the oxidative cross-linking portion of the stabilization reaction subsequently takes place.

Since the oxidative cross-linking reaction is accelerated in the present process, one optionally may elect to carry out the stabilization reaction at a less severe temperature than heretofore commonly utilized. Under milder temperature conditions a more uniform stabilized fiber may be achieved in the absence of undue chain degradation.

The stabilized fibrous material resulting from the stabilization treatment of the present invention is suitable for use in applications where a fire resistant fibrous material is required.

For instance, non-burning fabrics may be formed from the same. As previously indicated, the stabilized acrylic fibrous materials are particularly suited for use as intermediates in the production of carbonized fibrous materials. Such amorphous carbon or graphitic carbon fibrous products may be incorporated in a binder or matrix and serve as a reinforcing medium. The carbon fiber component may accordingly serve as a lightweight load bearing component in high performance composite structures which find particular utility in the aerospace industry.

The acceleration of the stabilization reaction is demonstrated by the following data. A continuous length of an 800 fil dry spun acrylonitrile homopolymer continuous filament yarn having a total denier of 1,200 was selected as the starting material. The yarn was dry spun from a solution of the same in N,N-dimethyl formamide solvent into an evaporative atmosphere of nitrogen. The fibrous material was dry spun as a 40 fil bundle, and plied to form the 800 fil yarn which exhibited a twist of about 0.5 t.p.i. The yarn was next drawn at a draw ratio of about 5:1 to a single filament tenacity of about 4 grams per denier by stretching while passing over a hot shoe at a temperature of about C. for a residence time of about 0.5 second. Two segments of the yarn were wound on two different porous bobbins and were given the following treatments: 1. Sample A was designated the control sample, and was placed in a circulating air oven at 250 C. for 30 minutes. At the end of this period of time a bound oxygen content within the fibrous material of 1.56 percent by weight as determined by the Unterzaucher analysis was observed.

2. Sample B was immersed in a vessel containing a 15 per cent aqueous solution of hydrogen peroxide provided at ambient temperature (i.e. about 25 C.) for 16 hours, was removed from the vessel, was allowed to dry at ambient conditions, was immersed in a vessel containing a l percent by weight aqueous solution of ferrous sulfate [FeSO -H O] provided at ambient temperature (i.e. about 25 C.) for 16 hours during which time a substantial quantity of molecular oxygen was generated in intimate association withthe fibrous material through the catalytic decomposition of hydrogen peroxide, and was placed in a circulating air oven at 250 C. for 30 minutes. At the end of this period of time a bound oxygen content within the fibrous material of 3.73 percent by weight as determined by the Unterzaucher analysis was observed.

The following examples are given as specific illustrations of the invention. It should be understood, however, that the invention is not limited to the specific details set forth in the examples.

EXAMPLE I A continuous length of an 800 fil dry spun acrylonitrile homopolymer continuous filament yarn having a total denier of 1,200 is selected as the starting material. The yarn is initially dry spun from a solution of the same in N,N-dimethyl formamide solvent into an evaporative atmosphere of nitrogen. The yarn is spun as a 40 fl] bundle, and plied to form the 800 fil yarn which exhibits a twist of about 0.5 t.p.i. The yarn is next drawn at a draw ratio of about 5:1 to a single filament tenacity of about 4 grams per denier by stretching while passing over a hot shoe at a temperature of about 160 C. for a residence time of about 0.5 second.

A sample of the yarn is wound upon a porous bobbin and is immersed in a vessel containing a 1 percent by weight aqueous solution of ferrous sulfate [FeSO -2H O] provided at ambient temperature (i.e. at about 25 C.) for 1 hour. The yarn is removed from the vessel and is allowed to dry at ambient conditions. The resulting yarn contains ferrous ions in intimate association therewith.

The yarn is immersed for 1 hour in a 15 percent by weight aqueous solution of hydrogen peroxide provided at ambient temperature (i.e. at about 25 C.). A substantial quantity of molecular oxygen is generated in intimate association with the acrylic fibrous material.

The resulting yarn is next placed in a circulating air oven at 250 C. for 90 minutes. Y

The stabilized yarn resulting from the treatment in the circulating air oven is black in appearance, retains its original fibrous configuration essentially intact, is non-burning when subjected to an ordinary match flame, and exhibits a bound oxygen content in excess of 7 percent by weight as determined by the Unterzaucher analysis.

EXAMPLE ll Example I is repeated with the exceptions indicated. The yarn while wound upon a porous bobbin is initially immersed in the aqueous hydrogen peroxide solution, allowed to dry at ambient conditions (i.e. at about 25 C.), and subsequently is immersed in the aqueous solution of ferrous sulfate.

Upon immersion in the aqueous solution of ferrous sulfate a substantial quantity of molecular oxygen is generated in intimate association with the acrylic fibrous material through the catalyzed decomposition of hydrogen peroxide.

Upon stabilization in the circulating air oven substantially similar results are achieved.

Although the invention has been described with preferred embodiments, it is to be understood that variations and modifications may be resorted to as will be apparent to those skilled in the art. Such variations and modifications are to be considered within the purview and scope of the claims appended hereto.

lCLAlM:

1. An improved process for the stabilization of an acrylic fibrous material selected from the group consisting of an 7 acrylonitrile homopolymer and acrylonitrile copolymers containing at least about 85 mol percent of acrylonitrile units and up to about 15 mol percent of one or more monovinyl units copolymerized therewith comprising:

a. contacting said acrylic fibrous material with an aqueous solution wherein a substantial quantity of molecular oxygen is generated in intimate association with said acrylic fibrous material through the catalyzed decomposition of hydrogen peroxide, and

b. heating the resulting acrylic fibrous material in an oxygen-containing atmosphere at a temperature of about 200 to 290 C. until a stabilized product is formed which retains its original fibrous configuration essentially intact and which is non-burning when subjected to an ordinary match flame, with said step (a) serving to accelerate the oxidative portion of the stabilization reaction during said heating.

2. A process according to claim 1 wherein said acrylic fibrous material is an acrylonitrile homopolymer.

3. A process according to claim 1 wherein said acrylic fibrous material is an acrylonitrile copolymer containing at least about 95 mol percent of acrylonitrile units and up to about 5 mol per cent of one or more monovinyl units copolymerized therewith.

4. A process according to claim 1 wherein said acrylic fibrous material has been drawn to a single filament tenacity of at least about 3 grams per denier.

5. A process according to claim 1 wherein said decomposition of hydrogen peroxide is catalyzed by metallic cations.

6. A process according to claim 1 wherein said decomposition of hydrogen peroxide is catalyzed by ferrous cations.

7. A process according to claim 1 wherein said acrylic fibrous material is provided in intimate association with metallic cations capable of catalyzing the decomposition of hydrogen peroxide prior to being contacted with an aqueous solution of hydrogen peroxide wherein a substantial quantity of molecular oxygen is generated in intimate association with said acrylic fibrous material.

8. A process according to claim 7 wherein said metallic cations are ferrous cations.

9. A process according to claim 1 wherein said acrylic fibrous material is provided in intimate association with hydrogen peroxide prior to being contacted with an aqueous solution containing metallic cations capable of catalyzing the decomposition of hydrogen peroxide wherein a substantial quantity of molecular oxygen is generated in intimate association with said acrylic fibrous material.

10. A process according to claim 9 wherein said metallic cations are ferrouscations.

11. A process according to claim 1 wherein said oxygencontaining atmosphere is at a temperature of about 220to 260 C.

12. A process according to claim 1 wherein said stabilized product exhibits a bound oxygen content of at least about 7 percent by weight, and a carbon content of about 50 to 65 percent by weight.

13. An improved process for the stabilization of an acrylic fibrous material selected from the group consisting of an acrylonitrile homopolymer and acrylonitrile copolymers containing at least about mol percent of acrylonitrile units and up to about 15 mol percent of one or more monovinyl units copolymerized therewith comprising:

a. contacting said acrylic fibrous material with an aqueous solution containing about 3 to 30 percent by weight hydrogen peroxide for a period of time sufficient to provide said hydrogen peroxide in intimate association with said acrylic fibrous material,

b. contacting said acrylic fibrous material while in intimate association with said hydrogen peroxide with an aqueous solution containing about 0.01 to 10 percent by weight ferrous sulfate wherein a substantial quantity of molecular oxygen is generated in intimate association with said acrylic fibrous material through the catalyzed decomposition of hydrogen peroxide, and

c. heating the resulting acrylic fibrous material in an oxygen-containing atmosphere at a temperature of about 200 to 290 C. until a stabilized product is formed which retains its original fibrous configuration essentially intact and which is non-burning when subjected to an ordinary match flame, with said step (b) serving to accelerate the oxidative portion of the stabilization reaction during said heating.

14. A process according to claim 13 wherein said acrylic fibrous material is an acrylonitrile homopolymer.

15. A process according to claim 13 wherein said acrylic fibrous material is an acrylonitrile copolymer containing at least about mol percent of acrylonitrile units and up to about 5 mol percent of one or more monovinyl units copolymerized therewith.

16. A process according to claim 13 wherein said acrylic fibrous material has been drawn to a single filament tenacity of at least about 3 grams per denier.

17. A process according to claim 13 wherein said acrylic fibrous material while in intimate association with hydrogen peroxide is immersed in said aqueous solution containing ferrous sulfate for at least about one hour.

18. A process according to claim 13 wherein said oxygencontaining atmosphere is at a temperature of about 220 to 260 C.

19. A process according to claim 13 wherein said oxygencont aining atmosphere is at a temperature of about 240 to 250 C.

20. A process according to claim 13 wherein said stabilized product contains a bound oxygen content of at least about 7 percent by weight, and a carbon content of about 50 to 65 percent by weight. 

2. A process according to claim 1 wherein said acrylic fibrous material is an acrylonitrile homopolymer.
 3. A process according to claim 1 wherein said acrylic fibrous material is an acrylonitrile copolymer containing at least about 95 mol percent of acrylonitrile units and up to about 5 mol per cent of one or more monovinyl units copolymerized therewith.
 4. A process according to claim 1 wherein said acrylic fibrous material has been drawn to a single filament tenacity of at least about 3 grams per denier.
 5. A process according to claim 1 wherein said decomposition of hydrogen peroxide is catalyzed by metallic cations.
 6. A process according to claim 1 wherein said decomposition of hydrogen peroxide is catalyzed by ferrous cations.
 7. A process according to claim 1 wherein said acrylic fibrous material is provided in intimate association with metallic cations capable of catalyzing the decomposition of hydrogen peroxide prior to being contacted with an aqueous solution of hydrogen peroxide wherein a substantial quantity of molecular oxygen is generated in intimate association with said acrylic fibrous material.
 8. A process according to claim 7 wherein said metallic cations are ferrous cations.
 9. A process according to claim 1 wherein said acrylic fibrous material is provided in intimate association with hydrogen peroxide prior to being contacted with an aqueous solution containing metallic cations capable of catalyzing the decomposition of hydrogen peroxide wherein a substantial quantity of molecular oxygen is generated in intimate association with said acrylic fibrous material.
 10. A process according to claim 9 wherein said metallic cations are ferrous cations.
 11. A process according to claim 1 wherein said oxygen-containing atmosphere is at a temperature of about 220* to 260* C.
 12. A process according to claim 1 wherein said stabilized product exhibits a bound oxygen content of at least about 7 percent by weight, and a carbon content of about 50 to 65 percent by weight.
 13. An improved process for the stabilization of an acrylic fibrous material selected from the group consisting of an acrylonitrile homopolymer and acrylonitrile copolymers containing at least about 85 mol percent of acryloNitrile units and up to about 15 mol percent of one or more monovinyl units copolymerized therewith comprising: a. contacting said acrylic fibrous material with an aqueous solution containing about 3 to 30 percent by weight hydrogen peroxide for a period of time sufficient to provide said hydrogen peroxide in intimate association with said acrylic fibrous material, b. contacting said acrylic fibrous material while in intimate association with said hydrogen peroxide with an aqueous solution containing about 0.01 to 10 percent by weight ferrous sulfate wherein a substantial quantity of molecular oxygen is generated in intimate association with said acrylic fibrous material through the catalyzed decomposition of hydrogen peroxide, and c. heating the resulting acrylic fibrous material in an oxygen-containing atmosphere at a temperature of about 200* to 290* C. until a stabilized product is formed which retains its original fibrous configuration essentially intact and which is non-burning when subjected to an ordinary match flame, with said step (b) serving to accelerate the oxidative portion of the stabilization reaction during said heating.
 14. A process according to claim 13 wherein said acrylic fibrous material is an acrylonitrile homopolymer.
 15. A process according to claim 13 wherein said acrylic fibrous material is an acrylonitrile copolymer containing at least about 95 mol percent of acrylonitrile units and up to about 5 mol percent of one or more monovinyl units copolymerized therewith.
 16. A process according to claim 13 wherein said acrylic fibrous material has been drawn to a single filament tenacity of at least about 3 grams per denier.
 17. A process according to claim 13 wherein said acrylic fibrous material while in intimate association with hydrogen peroxide is immersed in said aqueous solution containing ferrous sulfate for at least about one hour.
 18. A process according to claim 13 wherein said oxygen-containing atmosphere is at a temperature of about 220* to 260* C.
 19. A process according to claim 13 wherein said oxygen-containing atmosphere is at a temperature of about 240* to 250* C.
 20. A process according to claim 13 wherein said stabilized product contains a bound oxygen content of at least about 7 percent by weight, and a carbon content of about 50 to 65 percent by weight. 